1. Field of the Invention
The present invention relates to a crank angle detector for detecting an angle of a crankshaft of an engine.
2. Description of the Related Background Art
For controlling a fuel injection timing for supplying fuel to an engine by an injector or for controlling an ignition timing for discharging spark to an ignition plug, a rotating angular position from a reference position of a crankshaft of an engine, i.e., a crank angle is detected to set these timings based on the detected crank angle (see, for example, Laid-open Japanese Patent Application No. 63-263269 and Japanese Patent Publication No. 5-11562).
A conventional crank angle detector for detecting an angle of a crankshaft of an engine uses a disk-shaped rotary body adapted to rotate in association with rotation of the crankshaft, and an electromagnetic pickup positioned near the outer periphery of the rotary body. A plurality of convex portions made of a magnetic material are continuously arranged as portions to be detected on or near the outer periphery of the rotary body at predetermined angular intervals, where at least one convex portion is lacking in the regular arrangement. As the rotary body rotates in association with the crankshaft, the electromagnetic pickup generates a pulse each time a convex portion passes near the electromagnetic pickup. Since the lack of the convex portion results in a relatively long period in which no pulse is generated, the time at which a next pulse is generated is defined as a reference position time for a rotating angle of the crankshaft. A stroke of each cylinder is identified on the basis of the reference position.
In the conventional crank angle detector as mentioned above, however, the crankshaft does not rotate at a uniform speed during one rotation. Specifically, the rotating speed slightly varies depending on strokes such as a compression stroke, an explosion stroke, causing a pulse interval to correspondingly vary. Also, in addition to variations in the pulse interval during accelerating and decelerating operations, the pulse interval likewise varies particularly due to mechanical frictions in an engine when the engine is at low temperature. Thus, such variations, if appearing largely, makes unclear a time difference between a longer pulse interval due to the lacked convex portion and a normal pulse interval, leading to a failure in accurately identifying the reference position time of the rotating angle of the crankshaft.